Multiple station turret punch machines such as the Amada Lyla Series Model 50-50-72 can provide up to 72 different punch stations for use in conjunction with a like number of opposing die surfaces. In such a machine, each punch station includes a punch assembly and a punch guide. Even with the flexibility afforded by a 72-station machine, however, the operator may wish to change some or all of the punch and die combinations from time to time. For instance, the operator may wish to utilize a different punch tip shape or one of a different size. It is desirable to minimize the time required to so change the punch and die components, and thereby reduce down time for the punch machine.
In the punching operation, after the punch tip enters the worksheet surface, the edge of the cut surface will tend to follow the punch tip as it retracts. As a result, "stripping" occurs; that is, the edges around the punched hole will bear outwardly and necessitate further time consuming finishing operations.
To prevent stripping, the punch guide may be provided with a stripper plate. A stripper plate is a hardened plate having an opening such that a punch tip will fit snugly therethrough, yet be able to axially move freely through the opening. In use, the punch guide is oriented with the stripper plate flush against the worksheet surface. Then, when the punch tip retracts from the worksheet, the edges of the worksheet around the punch hole will be prevented by the stripper plate from following the retracting punch tip.
One such punch guide-stripper plate configuration incorporates the stripper plate as an integral part of the punch guide itself. Since the size and shape of the stripper plate hole must coincide closely with the punch tip, however, each such punch guide may only be used with one matching punch assembly. Consequently, interchanging punch and die combinations may be inconvenient, since the operator must change not only the die and the punch assembly, but the punch guide assembly as well.
Another configuration uses flattened metal clips or the like to retain a removable stripper plate at the end of a punch guide. This allows the use of a number of different punch tips with each guide, since only the stripper plate need be changed for each new punch tip. These spring clip structures, however, have not provided completely satisfactory. Often, the worksheet surface will have a thin coating of oil or other fluid. When the stripper plate meets the worksheet surface, a suction may be created. When this occurs, the stripper plate may be pulled out of place and damage may result to the worksheet and to the stripper plate. Down time may also become a problem. These clips also tend to weaken with usage, aggravating the above-noted problems. Another configuration is shown in U.S. Pat. No. 4,092,888 which depicts a punch guide assembly using a resilient retaining ring to hold a removable stripper plate in place.